CYTOKINE EXPRESSION IN HEPATOCYTES - ROLE OF OXIDANT STRESS

Inflammatory mediators, including cytokines and chemokines, are associ ated with the pathology of chronic liver disease. Interleukin-8 (IL-8) in humans and macrophage inflammatory protein-2 (MIP-2) in rodents, b oth members of the C-X-C family of chemokines, are particularly potent neutrophil attractants and have been implicated in chronic liver dise ases. In the liver, cytokine secretion is usually associated with nonp arenchymal cells, particularly Kupffer cells. In the present studies, chemokine gene expression and secretion were investigated in hepatocyt es treated with various stimulators. Using human Hep G2 cells, it was demonstrated that, in contrast to lipopolysaccharides (LPS), both tumo r necrosis factor-alpha (TNF-alpha) and H2O2 are potent inducers of IL -8, presumably acting via protein kinase C (PKC)-dependent pathways. M IP-2 expression occurred in freshly isolated rat hepatocytes following treatment with TNF-alpha, LPS, and to a lesser degree, H2O2, Both IL- 8 and MIP-2 secretion were inhibited, although to varying degrees, by such antioxidants as TMTU, DMSO, catalase, and N-acetylcysteine. Furth ermore, in vitro TNF-alpha neutralization experiments and transfection of Hep G2 cells with an IL-8 construct confirmed that TNF-alpha and H 2O2 directly stimulate IL-8 secretion. RT-PCR analyses indicated that chemokine secretion induced by these agents operates via increased gen e expression. Furthermore, a variety of cytokine genes were found to b e expressed by hepatocytes, including MCP-1, cytokine-induced neutroph il chemoattractant (CINC), and IL-6, Taken together, these studies ind icate that hepatocytes respond to biologically relevant levels of comm on activators, including H2O2, to produce cytokines and chemokines tha t contribute to pathophysiologic and repair processes in the liver.